Blow molded plastic container and method of making

ABSTRACT

A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, and a bottom portion. The bottom portion includes a central pushup area that is substantially symmetrical about the longitudinal axis and that is substantially flat. The pushup area preferably has a radius that is within the range of 0.100 inches to 0.500 inches. The bottom portion further includes a plurality of support feet surrounding and protruding downwardly from the pushup area, each of which has a bottom support surface and a pair of sidewalls that help define a valley between the support feet. The sidewalls have a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, and this angle is at least 25 degrees.

[0001] This is a continuation-in-part of Ser. No. 08/551,323, filed Nov.1, 1995, the disclosure of which is hereby incorporated as if it werefully set forth herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates broadly to the field of container making,and more specifically to blow molded plastic bottles, such as the PETbottles that are in common use today for packaging soft drinks such assoda.

[0004] 2. Description of the Prior Art and More Recent Technology

[0005] During the last twenty-five years or so, there has been adramatic shift in the packaging of carbonated beverages, particularly,soft drinks, away from glass containers and toward plastic containers.The plastic containers initially took the form of a two-piececonstruction, wherein a plastic bottle having a generally hemisphericalbottom was applied a separate base cup, which would permit the bottle tobe stood upright. The hemispherical bottom was seen as the mostdesirable shape for retaining the pressure generated by the carbonationwithin the container. Pressures in such containers can rise to 100p.s.i. or more when the bottled beverage is exposed to the sun, storedin a warm room, car trunk, or the like.

[0006] Such plastic containers represented a significant safetyadvantage over glass containers when exposed to the same internalpressures. However, the two-piece construction was not economicalbecause it required a post molding assembly step, and, also a separationstep prior to reclaiming or recycling the resins forming the bottle andbase cup.

[0007] During this period of development, various attempts were made toconstruct a one-piece, self-supporting container that would be able toretain the carbonated beverages at the pressures involved. Such aone-piece container requires the design of a base structure which willsupport the bottle in an upright position and will not bulge outwardlyat the bottom. A variety of designs were first attempted, with mostfollowing one of two principal lines of thought. One line of designsinvolved a so-called champagne base having a complete annular peripheralring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726;3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety ofdesigns is that which included a plurality of feet protruding downwardfrom a curved bottom. Examples of this variety are to be found in U.S.Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323. Inrecent years, the latter type of design has achieved primacy in themarketplace.

[0008] Footed one piece bottles present certain problems, though, whichhave not yet been worked out to the satisfaction of the packagingindustry and its customers. For example, the uneven orientation of thepolymer in the footed area of the bottom can contribute to uneven postfilling expansion of either one or more feet or the central portion ofthe bottom, creating what is generally referred to as a “rocker.” Inaddition, the presence of the feet themselves and the need to force theoriented material into the shape of the feet can create stress points inthe container bottom that can adversely affect container shape.Container bottom designs that minimize stress and disorientation of thepolymer during molding, then are considered preferable.

[0009] Another concern in the design of container bottoms for one piececontainers is the possibility of stress cracking in the base. The amountof stress cracking is related to the geometry of the base. Relativelylarge radius curves in the base will reduce the stress cracking comparedto a base with small radius curves.

[0010] Yet another factor that is important in the design of suchcontainers is volumetric and structural stability of the containerduring and after filling and pressurization of the container. Bulging ofvulnerable areas in the container bottom, particularly the pushup areain the center, will increase the volume of the container and affect thefilling process, as well as permit visible accumulation of gases at thetop of the bottle, which will be visible to the consumer. Suchdeformation is preferably to be avoided.

[0011] A need exists for an improved bottom design for a polymeric onepiece container that will optimize use of material relative to strength,reduce the possibility of stress cracking, reduce deformation duringfilling and storage, arid permit molding with a minimum of stress anddisorientation of the polymer material.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the invention to provide animproved bottom design for a polymeric one piece container that willoptimize use of material relative to strength, reduce the possibility ofstress cracking, reduce deformation during filling and storage, andpermit molding with a minimum of stress and disorientation of thepolymer material.

[0013] In order to achieve the above and other objects of the invention,a molded polymeric container that is shaped to be easier to mold, haveimproved rigidity under pressure and improved strength with respect tosuch containers heretofore known includes a substantially cylindricalbody portion having a longitudinal axis and a circumferential sidewall;and a bottom portion including a central pushup area that issubstantially symmetrical about the longitudinal axis, said pushup areabeing substantially flat and having a radius that is within the range of0.100 inches to 0.500 inches; a plurality of support feet surroundingand protruding downwardly from the pushup area, each of the support feethaving a bottom support surface and a pair of sidewalls, each of thesidewalls helping define a valley between said support feet, and whereinat least one of the sidewalls has a substantially straight portion thatdefines an angle with respect to a line that is perpendicular to thelongitudinal axis, the angle being at least 25 degrees; and a pluralityof ribs positioned in the valleys between the support feet, each of theribs being positioned between and helping to define two of the supportfeet.

[0014] According to a second aspect of the invention, a molded polymericcontainer that is shaped to be easier to mold, have improved rigidityunder pressure and improved strength with respect to such containersheretofore known includes a substantially cylindrical body portionhaving a longitudinal axis and a circumferential sidewall; and a bottomportion including a plurality of downwardly protruding support feet,each of the support feet having a bottom support surface and a pair ofsidewalls, each of the sidewalls helping define a valley between thesupport feet, and wherein at least one of the sidewalls has asubstantially straight portion that defines an angle with respect to aline that is perpendicular to the longitudinal axis, the angle being atleast 25 degrees, whereby the container bottom is easier to mold thanthose heretofore known.

[0015] These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a longitudinal cross-section of an improved polymericcontainer that is constructed according to a preferred embodiment of theinvention;

[0017]FIG. 2 is a close-up view of a bottom portion of what is depictedin FIG. 1;

[0018]FIG. 3 is a perspective depiction of the bottom of the containerthat is shown in FIGS. 1 and 2;

[0019]FIG. 4 is a side elevational depiction of the container bottomthat is shown in FIGS. 1-2;

[0020]FIG. 5 is a bottom plan view of the container bottom that is shownin FIGS. 14;

[0021]FIG. 6 is a longitudinal cross-section of a container that isconstructed according to a second embodiment of the invention; and

[0022]FIG. 7 is a fragmentary sectional view taken through one of theribs in the embodiment of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0023] Referring now to the drawings, wherein like reference numeralsdesignate corresponding structure throughout the views, and referring inparticular to FIGS. 1 and 2, a molded polymeric container 10 that isshaped to be easier is to mold, have improved rigidity under pressureand improved strength with respect to such containers heretofore known,includes, according to a preferred embodiment of the invention, asubstantially cylindrical body portion 12 that has a longitudinal axis18 and a circumferential sidewall 13. Sidewall 13 is separated from thelongitudinal axis 18 by a so-called label radius R_(L). As is typical insuch containers, polymeric container 10 includes a neck portion 14 thattapers into a threaded nipple that defines an opening 16. Container 10further includes a bottom portion 20 including a central pushup area 30that is substantially symmetrical about the longitudinal axis 18 of thecylindrical body portion 12 of the molded polymeric container 10. Bottomportion 20 further includes a plurality of support feet 22, of whichthere are five in the preferred embodiment, that surround and protrudedownwardly from the pushup area 30. Each of the support feet 22 has abottom support surface 24, shown in FIG. 2, that has radially inner edge26 and a radially outer edge 28, also shown in FIG. 2. The radiallyinner edges 26 of the respective support feet 22 together circumscribean inner ring 32, that is visible in FIG. 5 and has a radius R_(p) thatsurrounds the central pushup area 30. The support feet 22 extenddownwardly from a central point of the pushup area 30 by a longitudinaldistance D_(p).

[0024] The bottom portion 20 of the molded polymeric container 10further includes a plurality of ribs 34, each of which is positionedbetween and helps to define two of the support feet 22, as may be bestseen in FIGS. 3, 4 and 5. Each of the ribs 34 has a radius of curvatureR₅, as is shown diagrammatically in FIGS. 1 and 2.

[0025] As may be seen in FIG. 2, a whole cross section takenlongitudinal of the bottom portion 20 of container 10 will reveal thatthe support foot 22 is preferably formed with a first broad radiusedside surface that is curved at a first radius R₁, which merges into asecond, tighter radiused outer transition surface that has a curvatureradius R₂. The outer transition surface R₂ merges into the flat bottomsupport surface 24 at the outer edge 28, as may be clearly seen in FIG.2. At the inner edge 26 of the bottom support surface 24, the supportfoot 22 yields to a transition area 36 that is positioned between thecenter point of the pushup area 30 and the inner edge 26 or inner ring32 of the support foot 22. This transition area is characterized by acentral dome that has a lower concave surface that is curved at a radiusR₄, and a compensating area with a lower convex surface that curves at aradius R₃, and merges into the bottom of the support feet 22 at theinner edge 26 as shown in FIG. 2. Preferably, R₄ and R₃ should be noless than about 0.900 inches, and R₂ should be no less than about 0.500inches.

[0026] According to one important aspect of the invention, the radiusR_(p) of the pushup area 30 is between 10% to 50% of the radius R_(L) ofthe sidewall 13 of the body portion 12, so that the pushup area 30constitutes a relatively small proportion of the total area of thebottom portion 20. This reduces downward deflection of the pushup area30 when the container 10 is pressurized with, for example, a carbonatedbeverage. More preferably, the radius R_(p) of the pushup area 30 isbetween about 25% to about 47% of the radius R_(L) of the sidewall 13.Most preferably R_(p) is about 45% of the radius R_(L).

[0027] According to another important aspect of the invention, thelongitudinal distance D_(p) between the central point of the pushup area30 and the bottom of the support feet 22 is no more than 100% of theradius R_(p) of the pushup area 30. As a result of this, the transitionarea 36 that is defined between the central point and the inner ring 32is relatively shallow, thus reducing stresses in the transition area 36during use of the container and strengthening the container. Morepreferably, the distance D_(p) is between about 15% to about 50% of theradius R_(p), and is most preferably between about 22% to about 28% ofthe radius R_(p).

[0028] Another important feature of the invention is that the radius ofcurvature R₅, of the ribs 34 is no less than about 70% of the radiusR_(L) of the sidewall 13 of the body portion 12, so that the bottomportion 20 of the container 10 will be constrained to expandsubstantially hemispherically during molding, thereby orienting thepolymeric material in as relaxed a position as possible during molding,reducing stresses and optimizing the strength of the container bottom.More preferably, the radius of curvature R₅ of the ribs 34 is no lessthan about 90% of the radius R_(L) of the sidewall 13, and is mostpreferably no less than about 99% of the radius R_(L) of the sidewall13.

[0029] The longitudinal distance D_(p) between the central point of thepushup area 30 and the bottom of the support feet 22 is preferably nomore than about 0.5 inches, and may be as little as 0.15 inches. Theradius R_(p) between the longitudinal axis 18 and the inner ring 32 ofthe container bottom 20 may be as little as about 0.25 inches, and asgreat as about 1.2 inches. The smaller this dimension, the lessdeformation or bulging that is likely to occur when the container can ispressurized.

[0030] Preferably, container 10 is fabricated of PET. Alternatively, itmay be fabricated from PEN or a PEN-PET copolymer or physical blend ofthe two.

[0031] Container 10 may be molded according to known techniques from aparison in a mold that is contoured according to the dimensions andshape disclosed herein. During such molding, the bottom portion 20 ofthe container will be kept constrained in a substantiallyhemispherically shape because of the hemispherically shaped ribs 34 thathelp define support feet 22. Accordingly, molding will be accomplishedwith a minimum of disorientation and stress on the polymeric material.

[0032] A molded polymeric container 42 that is constructed according toa second aspect of the invention is depicted in FIGS. 6 and 7. Container42 includes a bottom portion 44 having a central pushup area 46 that issubstantially symmetrical about the longitudinal axis of the container42. The pushup area contains a substantially flat central portion 48,which has a radius R_(F) that is within the range of 0.100 inches to0.500 inches. More preferably the radius R_(F) is about 0.150 inches.The presence of the substantially flat area has been found to increasethe burst resistance of the container in the critical area near thecenter of the bottom portion 44. This area tends to be more susceptibleto bursting and stress cracking than other areas of the containerbottom, because the PET material in this area tends to be more amorphousand less oriented than at the other areas. The presence of the flat area48 avoids geometric points of stress concentration, which acts toincrease the burst resistance of the container bottom.

[0033] To avoid creating excessively severe transition angles 15(corresponding to reference number 36 in FIG. 2), the radius R_(p) ofthe pushup area 46 is may be increased by a distance that is equal tothe radius R_(F) of the flat portion 48.

[0034] Container 42 includes a plurality of support feet 22 surroundingand protruding downwardly from the pushup area 46. Each of the supportfeet 46 has a bottom support surface 24 and a pair of sidewalls 51, eachof the sidewalls 51 helping define a valley 56 between the support feet46, as may be seen in FIG. 7. At least one of the sidewalls 51 has asubstantially straight portion 52 that defines an angle α with respectto a line 50 that is perpendicular to the longitudinal axis of thecontainer 42. Angle α is at least 25 degrees and most preferably isabout 30 degrees. In the first embodiment described above, thecorresponding angle was only about 20 degrees. It has been found that byincreasing the angle α the moldability of the container increases, whichserves to permit more efficient manufacturing and lightweighting of thecontainer.

[0035] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A molded polymeric container that is shaped to beeasier to mold, have improved rigidity under pressure and improvedstrength with respect to such containers heretofore known, comprising: asubstantially cylindrical body portion having a longitudinal axis and acircumferential sidewall; and a bottom portion comprising: a centralpushup area that is substantially symmetrical about the longitudinalaxis, said pushup area being substantially flat and having a radius thatis within the range of 0.100 inches to 0.500 inches; a plurality ofsupport feet surrounding and protruding downwardly from the pushup area,each of the support feet having a bottom support surface and a pair ofsidewalls, each of said sidewalls helping define a valley between saidsupport feet, and wherein at least one of said sidewalls has asubstantially straight portion that defines an angle with respect to aline that is perpendicular to the longitudinal axis, said angle being atleast 25 degrees; and a plurality of ribs positioned in said valleysbetween said support feet, each of the ribs being positioned between andhelping to define two of the support feet.
 2. A container according toclaim 1, wherein said pushup area has a radius that is approximately0.150 inches.
 3. A container according to claim 1, wherein said angle isapproximately 30 degrees.
 4. A container according to claim 3, whereineach of said sidewalls contains a substantially straight portion.
 5. Acontainer according to claim 1, wherein each of said sidewalls containsa substantially straight portion.
 6. A molded polymeric container thatis shaped to be easier to mold, have improved rigidity under pressureand improved strength with respect to such containers heretofore known,comprising: a substantially cylindrical body portion having alongitudinal axis and a circumferential sidewall; and a bottom portioncomprising: a plurality of downwardly protruding support feet, each ofthe support feet having a bottom support surface and a pair ofsidewalls, each of said sidewalls helping define a valley between saidsupport feet, and wherein at least one of said sidewalls has asubstantially straight portion that defines an angle with respect to aline that is perpendicular to the longitudinal axis, said angle being atleast 25 degrees, whereby the container bottom is easier to mold thanthose heretofore known.
 7. A container according to claim 6, whereinsaid angle is approximately 30 degrees.
 8. A container according toclaim 8, wherein each of said sidewalls contains a substantiallystraight portion.